The present invention relates to a swash plate of a swash-plate type compressor. More particularly, the present invent ion relates to a surface-treating technique for outstandingly improving the sliding properties of a swash plate which consists of iron- based or aluminum-based material.
In the swash-plate type compressor, the swash plate 2 is rigidly secured obliquely to a rotary shaft 1 as shown in FIG. 1. Alternatively, the swash plate is secured obliquely to a rotary shaft in such a manner that its slanting angle is variable. The compression and expansion are carried out by means of rotating the swash-plate which increases or decreases the volume of partition space within a compressor, depending upon the rotation of the rotary shaft. Such swash plate is caused to slide on a shielding member referred to as a shoe 3. Gas-tight sealing between the swash plate and the shoe enables the compression and expansion of the cooling medium in the stated space. 4 is a ball.
A noteworthy point in the sliding conditions of a swash-plate is that, during the initial operational period of a compressor, the cooling medium reaches the sliding part prior to the lubricating oil reaching the sliding part between the swash plate and the shoe; thus the cooling medium has a rinsing effect on the lubricating oil which remains on the sliding part, with the result that the sliding condition is a dry condition free of lubricating oil. The sliding condition requirements of the swash plate are therefore very severe.
The sliding properties, which are required for a swash-plate used under the conditions described above, are seizure resistance, wear resistance, and the like. Proposals have thus been made to add hard matters into the aluminum material for enhancing the wear resistance, to improve the material of the swash plate, and to subject an iron-based swash-plate to heat treatment for enhancing the hardness and hence wear-resistance. In addition, the following surface treating methods are also proposed.
One of the present applicants proposed in Japanese Unexamined Patent Publication No. Sho51-36611 to bond the sintered Cu material on the shoe in the case of an iron-based swash plate. That is, an iron-based swash plate was heretofore subjected to hardening treatment. However, when the material of the opposed member, i.e., the shoe, is an iron-based material, the sliding takes place between identical kinds of materials thereby involving a problem that seizure is liable to occur. Sintered copper alloy is used for the opposing material (shoe) opposed to an iron-based swash plate, so as to avoid the above-mentioned problem.
In addition, it was also proposed to apply tin plating on the iron-based swash-plate so as to avoid the sliding between identical kinds of materials and hence to enhance the seizure resistance. Since the tin plating applied on an iron-based swash-plate is soft, a problem that arises is insufficient wear-resistance.
The eutectic or hyper-eutectic Alxe2x80x94Si based aluminum alloy, which is produced by casting or forging, exhibits excellent wear-resistance. Its production becomes, however, difficult, when the Si content exceeds 15%. The wear resistance of this alloy is, therefore, limited by the Si amount.
Recently, powder-metallurgy products utilizing a melt-quenched powder (for example Japanese Patent Publication No. 2535789) are proposed.
Since the Si content is very high, as much as from 14 to 30%, the wear resistance is greatly enhanced. However, the resultant alloy must be subjected to such working as hot-press followed by hot-extrusion. Therefore, in order to produce relatively large-sized parts, such as a swash plate, investment in installation of large-capacity equipment such as a press and an extruder is necessary. Cost competitiveness, therefore, is lowered.
It is, therefore, an object of the present invention to provide on the surface of an iron or aluminum-based swash-plate a surface-layer having improved both seizure-resistance and wear-resistance, thereby enhancing the performance and reliability of a swash-plate type compressor.
The present inventors carried out, therefore, research so that, the Alxe2x80x94Si aluminum-alloys based sliding material in a eutectic region or a hyper-eutectic region can be formed as a sliding layer on the surface of a swash plate by means of a simple method; and, considerably improved properties over those of the conventional various sliding layers are demonstrated.
The present inventors energetically carried out experiments and discovered that the flame-sprayed Alxe2x80x94Si based aluminum alloys in a eutectic region or a hyper-eutectic region exhibits improved adhesiveness with a substrate; and, the Si particles are refined. The present invention was thus completed.
Namely, the present first invention is a swash plate of a swash-plate type compressor, characterized in that a flame-sprayed layer deposited on the substrate contains from 12 to 60% by weight of Si, the balance being essentially Al, and has the granular Si particles dispersed in the matrix thereof. The present second invention is a swash plate of a swash-plate type compressor, characterized in that a flame-sprayed layer deposited on the substrate contains from 12 to 60% by weight of Si, from 0.1 to 30% by weight of Sn, the balance being essentially Al, and has the granular Si particles and Sn phase dispersed in the matrix thereof.
The flame-spraying (spraying) is based on the definition in the Glossary Dictionary of JIS Industrial Terms, 4 th edition, page 1946 and indicates that xe2x80x9cmaterial is converted to molten or half-molten state by a heat source and is blown onto a substrate to form a film.xe2x80x9d More specifically, the xe2x80x9cmaterialxe2x80x9d is aluminum-alloy or its raw material, for example, Al and Si powder. The half-molten state indicates such a solid-liquid coexisting state as is realized in a high-Si Alxe2x80x94Si alloy, i.e., a material having high melting-point. The half-molten state indicates that a portion of the powder does not melt, as is explained hereinbelow.
The present invention is explained in detail hereinafter. The percentage is weight % unless otherwise specified.
According to the Alxe2x80x94Si based alloy of the present first invention, Si in granular form is dispersed in the aluminum matrix finely and in a large amount. Thus, Si enhances the hardness and hence wear-resistance of the alloy. In addition, the granular Si particles disperse finely in a large amount and suppress the adhesion between the aluminum matrix and a shoe and hence seizure due to such adhesion.
EP 0713972A1 filed by the present applicants provides a detailed explanation of the flame-sprayed copper alloy by referring to an example of Cuxe2x80x94Pb alloy. The rapid cooling and solidification of molten particles is common in the Alxe2x80x94alloy example. One feature of the flame-sprayed Alxe2x80x94Si alloy is that an additive element (Si) has a higher melting point than that of the matrix element (Al). As a result, Si in granular form is finely dispersed in the aluminum matrix in a large amount. Thus, the effect is obtained such that Si enhances the hardness and hence wear-resistance of the alloy.
In the present invention, the granular Si particles do not have the same shape as seen in the primary Si of the conventional melted alloy or the Si particles of the rolled alloy. They have a one-directional, lengthwise property. Rather, the granular Si particles of the present invention have spheroidal, nodular, polygonal or irregular shapes, not classified as the former three shapes, and have almost the same size in any direction. Furthermore, a noteworthy distinction between the primary Si and eutectic Si seen in the conventional melted alloys disappears in the case of the present invention.
When the Si content of the aluminum-alloy according to the present invention is less than 12%, the enhancement effects of wear resistance and seizure resistance are slight. On the other hand, when the Si content exceeds 60%, the strength so drastically lowers as to impair wear resistance. A preferable Si content is from 15 to 50%. When the size of Si particles exceeds 50 xcexcm, separation of the Si particles is liable to occur. A preferable size is from 1 to 40 xcexcm.
Next, the Alxe2x80x94Sixe2x80x94Sn based alloy of the present second invention exhibits improved wear-resistance and seizure-resistance. The shape and content of Si as in the description of the first invention are common. Sn is a component for imparting the lubricating property and compatibility. Sn preferentially adheres to the shoe and impedes the sliding of materials of the same kind, i.e., Al adhering to the Al of the bearing, with the result that the seizure resistance is enhanced. When the Sn content is less than 0.1%, it is not effective for enhancing the lubricating property and the like. On the other hand, when the Sn content exceeds 30%, the strength of the alloy is lowered. A preferable Sn content is from 5 to 25%. The morphology of the Sn phase in the layer is elongated flaky. This morphology seems to be preferable in the light of the lubricating property.
The aluminum alloy according to the present first and second invention can contain the following optional elements.
Cu: Cu is solid-dissolved in the aluminum matrix at super-saturation and thus enhances its strength. Cu thus suppresses adhesive wear of aluminum and wear due to separation of Si particles. In addition, a part of Cu forms with Sn, a Snxe2x80x94Cu intermetallic compound and hence enhances the wear-resistance. However, when the Cu content exceeds 7.0%, the alloy is hardened too much to provide appropriate sliding material. A preferable Cu content is from 0.5 to 5%.
Mg: Mg is combined with a part of Si and forms an Mgxe2x80x94Si intermetallic compound. Mg, thus, enhances the wear resistance. However, when the Mg content exceeds 5.0%, the coarse Mg phase formed impairs the sliding properties.
Mn: Mn is solid-dissolved in the aluminum matrix at super-saturation and thus enhances its strength. The effects attained by Mn are the same as those by Cu. However, when the Mn content exceeds 1.5%, the alloy is hardened too much to provide appropriate sliding material. A preferable Mn content is from 0.1 to 1%.
Fe: Fe is solid-dissolved in the aluminum matrix at super-saturation and thus enhances its strength. The effects attained by Fe are the same as those by Cu. However, when the Fe content exceeds 1.5%, the alloy is hardened too much to provide appropriate sliding material. A preferable Fe content is from 0.1 to 1%.
Ni: Ni is solid-dissolved in the aluminum matrix at super-saturation and thus enhances its strength. The effects attained by Ni are the same as those by Cu. However, when the Ni content exceeds 8%, the alloy is too hardened to provide appropriate sliding material. A preferable Ni content is from 0.1 to 5%.
Subsequently, the formation of a sliding layer by flame spraying, which is common in the present first and second invention, is described.
In the present invention, various flame-spraying methods listed in FIG. 2 of Tribologist, ibid. page 20, FIG. 2 can be employed. Among them, the high-velocity oxyfuel flame-spraying method (HVOF, high velocity oxyfuel) can be preferably employed. It seems that the characterizing morphology of the Si and Sn phases can be obtained by this method, since it has the features described on page 20, right-hand column, lines 4 through 13 of Tribologist, ibid. Flame-sprayed Al is so rapidly cooled and solidified that a large amount of Si is solid-dissolved to harden Al. It has, therefore, the feature of holding the Si particles at high strength. Separation of Si particles and the wear due to such separation can, therefore, be suppressed.
An atomized powder of alloys such as Alxe2x80x94Si alloy, Alxe2x80x94Sixe2x80x94Sn alloy and the like can be used as the flame-spraying powder. These atomized powders may be completely melted on the substrate and then solidified.
Alternatively, a partly unmelted atomized powder may be applied on the substrate, so that the unmelted structure of powder remains.
The flame-spraying conditions are preferably: from 0.45 to 0.76 MPa of the oxygen pressure; from 0.45 to 0.76 MPa of fuel pressure; and from 50 to 250 mm of flame-spraying distance. A preferable thickness of the flame-sprayed layer is from 10 to 500 xcexcm, particularly from 10 to 300 xcexcm.
The hardness of the flame-sprayed alloy is in a range of from Hv100 to 600. Since the hardness of the conventional 12% Si-containing alloy is Hv70 to 150, the flame-sprayed layer according to the present invention can be said to be very hard.
Various metal substrates, such as iron, copper, aluminum and the like can be used as the substrate to form a flame-sprayed alloy thereon.
When the surface of a substrate is roughened by means of shot-blasting and the like, to preferably Rz 10 to 60 xcexcm of surface roughness, then the adhesive strength of the film can be increased. More specifically, the measurement of adhesive strength of a film by a shear-fracture testing method revealed that: adhesive strength of a flame-sprayed Ni film on the shot-blasted steel substrate was 30 to 50 MPa; while the adhesive strength of the film according to the present invention was 40 to 60 MPa. This is higher than that of the flame-sprayed Ni film, which has been heretofore reputed to have good adhesiveness.
Heat treatment can be applied to the flame-sprayed alloy to adjust the hardness.
The adhesion strength of the flame-sprayed layer and substrate is created by the alloy formation between the aluminum (that is, the matrix of the flame-sprayed layer) and the metal of the substrate which fuse and diffuse with one another. On the other hand, a dispersion phase such as Si, seems to lack such function and hence does not contribute to the adhesion strength. Since Sn and Si tend to decrease the adhesiveness as described above, the adhesion strength can be enhanced by means of forming such a concentration gradient so that the concentration of these elements increases continuously or non-continuously in the direction from the substrate side toward the surface. As a result, the flame-sprayed layer in contact with the substrate is of a pure Al alloy having a low concentration of the secondary-phase forming element such as Si. Such a concentration gradient can be formed by means of varying the blending composition of the flame-spraying powder.
In the case of using the flame-sprayed alloy without application of an overlay, the flame-sprayed surface is preferably finished to Rz 3.2 xcexcm or less. In the case of using the overlay, various soft coatings exhibiting excellent compatibility, such as Sn, Pbxe2x80x94Sn, MoS2, and MoS2-graphite-based coating, can be used so as to enhance the seizure-resistance.
The shoe per se is known. It is shown for example in Japanese Unexamined Patent Publication No. 51-36611 filed by the present applicants. Any material, of which the main component is iron, can be used as the iron-based material. Bearing steel is, however, preferable. In addition, the production method of a shoe is not at all limited. Such techniques as rolling, forging, powder-metallurgy, surface-hardening can be optionally employed.
The present invention is described by way of examples.